7. Выполнить умножение: a 4 21. ) 7 6 15. ) 10 B 15 14 ) 21 25 г) 4 6 1--.7 9 д 1 4 2--.2-- 2 5 e 5 1 8--.2-- 9 22

7. Выполнить умножение:

a) 21 \(\cdot\) \frac{4}{7} = \frac{21}{1} \(\cdot\) \frac{4}{7} = \frac{21 \(\cdot\) 4}{1 \(\cdot\) 7} = \frac{84}{7} = 12

б) 15 \(\cdot\) \frac{6}{10} = \frac{15}{1} \(\cdot\) \frac{6}{10} = \frac{15 \(\cdot\) 6}{1 \(\cdot\) 10} = \frac{90}{10} = 9

в) \frac{15}{21} \(\cdot\) \frac{14}{25} = \frac{15 \(\cdot\) 14}{21 \(\cdot\) 25} = \frac{3 \(\cdot\) 5 \(\cdot\) 2 \(\cdot\) 7}{3 \(\cdot\) 7 \(\cdot\) 5 \(\cdot\) 5} = \frac{2}{5}

г) 1\frac{4}{9} \(\cdot\) \frac{6}{7} = \frac{13}{9} \(\cdot\) \frac{6}{7} = \frac{13 \(\cdot\) 6}{9 \(\cdot\) 7} = \frac{13 \(\cdot\) 2 \(\cdot\) 3}{3 \(\cdot\) 3 \(\cdot\) 7} = \frac{26}{21} = 1\frac{5}{21}

д) 2\frac{1}{2} \(\cdot\) 2\frac{4}{5} = \frac{5}{2} \(\cdot\) \frac{14}{5} = \frac{5 \(\cdot\) 14}{2 \(\cdot\) 5} = \frac{14}{2} = 7

е) 8\frac{5}{9} \(\cdot\) 2\frac{1}{22} = \frac{77}{9} \(\cdot\) \frac{45}{22} = \frac{77 \(\cdot\) 45}{9 \(\cdot\) 22} = \frac{7 \(\cdot\) 11 \(\cdot\) 5 \(\cdot\) 9}{9 \(\cdot\) 2 \(\cdot\) 11} = \frac{7 \(\cdot\) 5}{2} = \frac{35}{2} = 17\frac{1}{2}

Ответ: а) 12, б) 9, в) \(\frac{2}{5}\), г) 1\(\frac{5}{21}\), д) 7, е) 17\(\frac{1}{2}\)

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